PROJECT SUMMARY/ABSTRACT Squamous Cell Carcinoma (SCC) is a common cancer that develops in stratified epithelial tissues such as the epidermis, the oral cavity, and the lungs. Standard treatments for patients with un-resectable SCC, which include radiation, cis-platin, 5-fluorouracil, and paclitaxel, are only modestly effective, resulting in approximately 45,000 deaths every year. While there has been some progress in the development of target therapies, such as EGFR inhibition, these treatments have not shown the efficacy seen in other tumors such as lung Adenocarcinoma. Recent advances in immunotherapy have shown great promise in treating SCC, even at advanced stage, but like many other tumor types only a minority of SCC patients respond to immunotherapy. In addition, the risk of cutaneous SCC is greatly increased in immunosuppressed transplant recipients, who are poor candidates for immunotherapy. This project aims to identify novel therapeutic targets that mediate resistance to FGFR inhibition in SCC. We will employ an orthotopic transplant model system that is driven by genetic alterations commonly found in human SCC tumors. A drop-out screen using a CRISPR/Cas9 library will be performed in vivo using orthotopic tumors. Hits will be validated using in vitro and in vivo SCC model systems employing either shRNA or CRISPR/Cas9-based target gene knockdown, as well as available antibody-based or small molecule inhibitors. In addition, we will validate the expression of potential targets human SCC tumors by Tissue Microarray, which will help to identify clinical characteristics of patients that may benefit from this therapeutic strategy. There are many drugs that are FDA-approved or in clinical trials that have not been tested for cooperation with FGFR inhibition, and thus this un-biased approach is likely to uncover unexpected vulnerabilities that can be rapidly translated into treatments for SCC patients.